Manually operated industrial shut-off valves have been in use for over 100 years to control flow through commercial and industrial fluid flow systems including water systems, a wide variety of chemical systems, and industrial fluid processing systems. Typically, these valves are inline valves having a valve body with approximately coaxial inlets and outlets separated by an integral dividing wall having a valve seat against which a valve member seats. Typically this valve member is axially movable by a valve stem threaded into a bonnet which projects transversely outwardly from the valve body, or in other words, perpendicular to the associated fluid flow line. A hand wheel is attached to the projecting end of the valve stem for manual rotation.
By far the most common sealing system for preventing leakage between the valve stem and the bonnet has in the past taken the form of axially compressible packing materials. These materials are typically a fabric composition, asbestos, or leather, and in some cases a synthetic composite, all generally in annular configuration.
The packing material is usually seated in a counter bore in the bonnet surrounding the valve stem, and it is axially compressed by a packing nut also surrounding the valve stem and threaded into the distal end of the bonnet. The sealing efficacy is adjusted by rotating the packing nut to axially compress the packing material, which upon compression expands radially into progressively tighter engagement with the periphery of the valve stem.
A long-standing problem with this type of packing system is that in order to prevent fluid leakage along the stem from the valve body, it is necessary that the packing nut be driven into the packing material to such an extent that manual rotation of the valve stem is either very difficult or even impossible without loosening the packing nut. And of course, if the packing nut is loosened to permit hand wheel rotation, fluid leaks along the valve stem while the valve is opening or closing.
Another problem with these packing material sealing systems is that they are subject to wear and frequent replacement in applications where the valve is opened and closed frequently.
There have in the past been attempts to reduce or ameliorate these sealing problems with the provision of more than one seal around the valve stem.
One such multiple seal system is shown in the Hansen, U.S. Pat. No. 4,550,896, in which a packing material type seal is supplemented by an axially spaced "O" ring in a counter bore below and spaced from the packing material by a flat washer.
In the Hansen design, a packing nut directly engages and compresses the top of the packing material. While the Hansen system increases the overall sealing efficiency over packing material alone designs, it does not alleviate the problem of over-compression of the packing material and its resulting difficulty in rotating the valve stem to effect valve operation.
Furthermore, the single "O" ring design of Hansen results in "O" ring wear, and the "O" ring is extremely difficult to replace because it is below the packing material in a counter bore in the bonnet so that the packing nut, and the difficult to remove packing material, must be withdrawn from the counter bore each time the "O" ring seal is to be replaced.
It is a primary object of the present invention to ameliorate the problems noted above in packing systems for shut-off valves.